Flame retardant modified polyphenylene oxide composition

Abstract

It was unexpectedly found that a brominated phosphate ester, tris(2,4-dibromophenyl)phosphate when employed in flame retardant quantities in a modified polyphenylene oxide resin resulted in discoloration of the resin on aging. Neither phosphate esters, flame retardants nor brominated flame retardants when employed separately as flame retardants caused similar discoloration. The use of epoxy compounds counteracted this color stability problem.

Description

The present invention is a modified polyphenylene oxide resin composition containing a brominated phosphate ester as a flame retardant. The composition has a reduced tendency to discolor when aged.

Polyphenylene oxide (also called polyphenylene ether) when combined with polystyrene forms a family of thermoplastic engineering resins called modified polyphenylene oxide. The compositions can be varied to adjust the mechanical properties of the finished resin product and vary the processability of the resin for injection molding and extruding and the like.

Polyphenylene oxide is produced from the oxidative coupling polymerization of 2,6-dimethylphenol. It is a linear amorphous polymer with a glass transition temperature of about 210.degree. C.

Flame retardant grades of polyphenylene oxide resins modified with polystyrene can be produced by incorporating conventional additives. Examples include brominated polystyrene, phosphate esters and an oligomer of tetrabromobisphenol A.

Recently a flame retardant polybromophenyl phosphate additive has been proposed in U.S. Pat. No. 4,710,530 for modified polyphenylene oxide, in particular, tris(2,4-dibromophenyl)phosphate. These flame retardants have low volatility and contain both phosphorus and bromine.

Unexpectedly it has been found that the color stability of a modified polyphenylene oxide resin containing a flame retardant amount of a brominated phosphate ester may be significantly improved by incorporating a color stabilizing amount of an epoxy compound. The improvement in color stability is clearly evident in accelerated aging tests at elevated temperatures. Color stability is particularly important when the resin composition is fabricated into a decorative article.

The present invention is a flame retarded polyphenylene oxide composition comprising a polystyrene modified polyphenylene oxide resin, a flame retardant amount of a polybrominated aryl phosphate ester, and a sufficient quantity of an epoxy compound to enhance the color stability of the flame retarded polyphenylene oxide composition.

Other conventional additives for modified polyphenylene oxide resins may be incorporated into the flame retarded polyphenylene oxide composition without adversely affecting the flame retardancy or color stability of the modified polyphenylene oxide resin. These additives include stabilizers, fillers, foaming agents and the like.

Generally it is desirable to incorporate up to 15 phr (parts per hundred parts of resin) of the polybrominated aryl phosphate into the modified polyphenylene oxide resin. Although more than 15 phr of the polybrominated aryl phosphate is effective, amounts in excess of 15 phr are usually not necessary to obtain a V-0 rating.

A particularly desirable polybrominated aryl phosphate ester is tris(2,4-dibromophenyl)phosphate.

Any epoxy compound suitable for incorporation into a polymeric resin appears to be effective in improving the color stability of the flame retarded modified polyphenylene oxide. Examples include such extremes as epoxidized soybean oil, epoxidized linseed oil and 3,4-epoxycyclohexyl methyl-3,4-epoxy cyclohexane carboxylate, a diepoxide. The efficacy of the epoxide employed appears to be proportional to the oxirane content. Therefore, one skilled in the art can readily determine the optional composition for any particular application by balancing the effect of the cost of the epoxide, the oxirane content of the epoxide and the effect of the epoxide on the other physical properties of the modified polyphenylene oxide resin. It is generally desirable to add an epoxy compound containing 6% to 12% oxirane oxygen at a rate of 1 phr to 5 phr.

Epoxy compounds are normally employed in polyvinyl compounds as plasticizers and stabilizers. However, until the present invention there has been no suggestion to employ epoxides for any purpose in modified polyphenylene oxide resins.

The best mode for practicing the present invention will be clear to one skilled in the art from the following nonlimiting examples.

Color was measured as the yellowness index by a reflective spectrophotometer (Elrepho 2000) manufactured by Carl Zeiss Co.

EXAMPLE A

The color instability problem is illustrated in Table I. The yellowness index of modified polyphenylene oxide compositions formulated with 12 phr (12 parts of flame retardant per hundred parts of resin) of different flame retardants was determined before and after accelerated aging at 115.degree. C. The flame retardants employed were: an alkylated triarylphosphate ester (TAP), brominated polystyrene, a polycarbonate oligomer of tetrabromobisphenol A (BPAC), tris(2,4-dibromophenyl)phosphate (TDBP), and bis(tribromophenoxy)ethane (BTBE). Table I shows that the composition initially was significantly yellower than the comparative compositions. After six days at 115.degree. C. the TDBP composition had further increased in yellowness compared with the comparative compositions.

EXAMPLE 1

Compositions of modified polyphenylene oxide (G.E. Noryl ENG-265) with 12 phr TDBP were prepared with various commercial stabilizers as additives and with several epoxides in a screening test. The yellowness index was determined as in Example A. Compositions and results are presented as Table II. Tradenames and common abbreviations of additives follow:

DPDP--Diphenyl isodecyl phosphite (Borg-Warner Corporation), TRIBASE EXL--Modified tribasic lead sulfate (National Lead Company), TEA--Triethanolamine, Naugard 445--Aromatic amine antioxidant (Uniroyal Chemical), Naugard SP--Antioxidant (Uniroyal Chemical), Irganox 1010--Hindered phenol antioxidant (Ciba-Geigy Corporation) AM 545--Stabilizer for halogen containing polymers (Ferro Corporation), Ferro 75001--Ba/Cd stabilizer (Ferro Corporation), B.sub.2 0.sub.3 --Boric oxide, ESO--Epoxidized soybean oil, ERL-4221--3,4-epoxycyclohexyl methyl3,4-epoxy cyclohexane carboxylate (Union Carbide Corporation), TiO.sub.2 --Titanium dioxide, CaCo.sub.3 --Calcium carbonate, MgO--Magnesium oxide, and ZnO--Zinc oxide.

From Table II it is clear that ERL-4221 reduces yellowness on both the initial and aged samples. Samples 16-18 suggest the ESO also has some benefit.

EXAMPLE 2

The effect of the ERL-4221 diepoxide on color stability was confirmed in a test after aging 26 days at 80.degree. C. Compositions and results are presented as Table III.

EXAMPLE 3

Example 2 was repeated with the compositions being aged 16 days at 95.degree. C. and 11 days at 115.degree. C. Results are presented as Table IV. A polycarbonate oligomer of tetrabromobisphenol A (BPAC) was also included.

EXAMPLE 4

Example 2 was repeated at 80.degree. C. and 115.degree. C. The example demonstrates that 0.5 phr DPDP is ineffective compared with 3 phr diepoxide on the color stability of tris(2,4-dibromophenyl)phosphate. Results are presented as Table V. These data show the DPDP (phosphite) to be ineffective.

EXAMPLE 5

Yellowness indices were determined using GE Noryl PX 844 modified polyphenylene oxide and a variety of flame retardants and stabilizers. Results are presented as Table VI. These data show that both epoxidized soybean oil and the ERL-4221 diepoxide are effective stabilizers.

EXAMPLE 6

Various epoxy compounds were employed as color stabilizer for GE Noryl ENG-265 polyphenylene oxide containing 12 phr tris(2,4-dibromophenyl)phosphate. Additives and results are presented as Table VII. This example shows the efficacy of the epoxy compound is proportional to its oxirane content.

EXAMPLE 7

ESO containing 6.8% oxirane oxygen at 1,3 and 5 phr and 3 phr diepoxide with an 11-12% oxirane oxygen were compared in a Noryl ENG-265 polyphenylene oxide composition containing 12 phr tris(2,4-dibromophenyl)phosphate. Results are presented as Table VIII.

TABLE I______________________________________COLOR OF MODIFIED POLYPHENYLENE OXIDECOMPOSITIONS AGED AT 115.degree. C. CONTAINING12 PHR FLAME RETARDANTS Yellowness Index Initial 60 Days______________________________________Alkylated Triarylphosphate 12.5 18.5Brominated Polystyrene 16.3 25.2Bis(tribromophenoxy)ethane 15.5 24.7Tris(2,4-dibromophenyl) 22.7 36.5phosphate______________________________________ TABLE II______________________________________COLOR ON AGING AT 115.degree. C. OF MODIFIEDPOLYPHENYLENE OXIDE WITH 12 PHR TRIS(2,4-DIBROMOPHENYL)PHOSPHATEAdditiveSample Trade Desig- YellownessNo. phr nation Initial 8 Day 12 Day______________________________________ 1 0 CONTROL 20.7 33.4 39.2 2 1 TiO.sub.2 21.2 33.5 38.2 3 1 CaCo.sub.3 22.4 33.8 38.0 4 0.5 MgO 18.9 34.5 51.2 5 0.3 ZnO 20.8 36.7* -- 6 0.3 ZnO 0.5 DPDP 20.0 36.6* -- 7 1 B.sub.2 O.sub.3 24.5 33.9 41.2 8 1 Tribase EXL 15.6 32.5 36.0 9 1 B.sub.2 O.sub.3 1 TEA 20.4 33.5 39.110 1 Naugard 445 20.5 36.7 39.211 0.5 DPDP 0.5 Irganox 1010 16.8 35.7 41.012 0.5 DPDP 0.5 Naugard SP 21.5 37.8 41.813 0.5 DPDP 2 B.sub.2 O.sub.3 18.6 31.7 38.914 0.5 DPDP 0.5 Irganox 1010 1 Naugard 445 16.3 32.3 38.715 0.5 DPDP 0.5 Irganox 1010 1 Naugard 445 1 TiO.sub.2 20.7 35.7 40.116 3 ESO 19.1 34.8 40.6 0.5 DPDP 0.5 Irganox 1010 1 Naugard 445 1 TiO.sub.2 20.7 35.7 40.117 3 ESO 18.1 26.7 44.6 1 Ferro-75001 0.5 DPDP 0.5 Irganox 1010 1 Naugard 445 1 TiO.sub.2 20.7 35.7 40.118 3 ESO 1 AM-545 13.5 29.3 40.019 3 ERL-4221 13.9 22.2 27.7______________________________________ *6 days TABLE III______________________________________COLOR OF MODIFIED POLYPHENYLENE OXIDECOMPOSITIONS AGED AT 80.degree. C. Yellowness IndexAdditive Initial 26 Days______________________________________12 phr Triarylphosphate 11.3 17.412 phr Brominated 15.3 17.9Polycarbonate (BPAC)12 phr TDBP 16.2 23.412 phr TDBP and 11.4 16.73 phr ERL-4221______________________________________ TABLE IV______________________________________COLOR OF MODIFIED POLYPHENYLENE OXIDECOMPOSITIONS AGED AT 95.degree. C. AND 115.degree. C. Yellowness Index 6 Days 11 DaysAdditive Initial at 95.degree. C. at 115.degree. C.______________________________________12 phr Triarylphosphate 10.8 17.3 --12 phr Tetrabromobis- 13.4 17.0 23.8phenol A Oligomer12 phr Brominated 13.7 20.0 25.3Polystyrene12 phr TDBP 15.6 28.3 37.012 phr TDBP and 3 phr ERL 12.8 18.3 23.9______________________________________ TABLE V______________________________________EFFECT OF EPOXIDE ON THE COLOR STABILITYOF MODIFIED POLYPHENYLENE Yellowness Index 33 Days 10 Days 6 DaysAdditive Initial at 80.degree. C. at 95.degree. C. at 115.degree. C.______________________________________Triarylphosphate 12 -- 15 19Brominated Poly- 16 -- 19 25styreneTDBP 22 33 29 37TDBP and 0.5-DPDP 20 32 27 37TDBP and 3-ERL- 13 19 22 234221______________________________________ TABLE VI______________________________________COLOR STABILITY OF FLAME RETARDANTNORYL PX844 MODIFIED POLYPHENYLENEOXIDE COMPOSITION AND 12 phr TDBP12 phr Flame Yellowness IndexRetardant Initial 5 Days 9 Days 19 Days______________________________________Triarylphosphate 23.5 25.6 30.3 33.1esterBrominated Poly- 21.7 25.7 26.1 30.6styreneTetrabromobis- 23.4 28.7 29.3 33.8phenol oligomerTDBP 28.3 31.0 36.1 39.8TDBP with 1 phr 27.6 31.4 32.8 40.0B.sub.2 O.sub.3TDBP with 3 phr 15.5 21.6 25.8 32.5ESOTDBP with 3 phr 17.3 19.9 21.2 25.7ERL-4221______________________________________ TABLE VII______________________________________COLOR STABILIZATION OF FLAMERETARDED NORYL ENG-265 POLYPHENYLENEOXIDE EPOXY COMPOUNDSAND 12 phr TDBP Yellowness Index 18 DaysEpoxy Compound Oxirane Oxygen Initial at 95.degree. C.______________________________________None 0 15.6 28.33 phr Epoxy Soybean 6.8 14.1 26.7Oil3 phr 828 (Shell) 7.6 to 9.1 16.1 24.43 phr Epoxy Linseed 9 17.0 24.9Oil3 phr ERL-4221 11 to 12 12.8 18.3(Union Carbide)______________________________________ TABLE VIII______________________________________COLOR STABILIZATION OF FLAME RETARDEDMODIFIED POLYPHENYLENE OXIDE CONTAINING12 phr TRIS(2,4-DIBROMOPHENYL)PHOSPHATE Yellowness IndexStabilizer phr Initial 32 Days at 80.degree. C.______________________________________ESO 1 16.6 29.8ESO 3 12.4 26.5ESO 5 12.8 21.5ERL-4221 3 12.2 19.1______________________________________

Claims

1. A flame retarded polyphenylene oxide composition comprising a polystyrene modified polyphenylene oxide resin, a flame retardant amount of a polybrominated aryl phosphate ester, and a sufficient quantity of an epoxy compound to enhance the color stability of the flame retarded polyphenylene oxide composition.

2. The composition of claim 1 wherein the polybrominated aryl phosphate ester is tris( 2,4-dibromophenyl)phosphate.

3. The composition of claim 1 wherein an epoxy compound containing 6% to 12% oxirane oxygen is incorporated at a rate of from 1 phr to 5 phr.

4. The composition of claim 2 wherein an epoxy compound containing 6% to 12% oxirane oxygen is incorporated at a rate of from 1 phr to 5 phr.

5. The composition of claim 1 wherein the flame retarded polyphenylene oxide composition contains up to about 15 phr tris(2,4-dibromophenyl)phosphate.

6. The composition of claim 5 wherein an epoxy compound containing 6% to 12% oxirane oxygen is incorporated at a rate of from 1 phr to 5 phr.